Magnetic permeability indicator



. Y 1943- r w. A. BRUCE v 2,318,666

MAGNETIC PERMEABILI TY INDICATOR v Filed Nov. 12, 1940 l8 4 32 22 g IO 2| 23 .22\ 3 d. INVENTOR.

.Jii BY g We? permeability, and particularly welded joints.

Patented May 11, 1943 I UNITED STAT ES PATENT OFFICE MAGNETIC PERMEABILITY, mpica'ron William A. Bruce, Tulsa, Okla", assignor to Standard Oil Development Company, a corporation of Delaware Application November 12,1940, Serial No. 365,175

1 Claim. (01. 175-183) that the magnetic permeability of the weld changes with the molecular changes of the metal,

and registers a sharp increase at the aforesaid.

critical point. The practice,thereiore, has been developed of observing the magnetic permeability of welded joints during their cooling so as to determine when the critical point is reached.

The principal object ofthe present invention is the provision of a device adapted to be carried in the pocket for testing metals for magnetic A particular object of the present invention is the provision of a device of the character described having an electrical signalling means and e an electrical circuit for operating said means including a magnetic switch in the magnetic circuit of which the metal to be tested is adapted to be included whereby. when the permeability of flange II and an annular portion i 2 forming with y the outer end of the casing l a seat for a glass head I3 held in place by a set screw it. The inner portion of the annular end' l2 forms a seat for a light socket it in which is arranged a light bulb ll.

' Welded to the lower end of the light socket is a spring l8 arranged in the bore of member I0 and being coextensive therewith. The other end of the spring is connected to the head IQ of a rod slidably mounted in the tube 5, and made of soft iron. At its upper end the rod 28 has a flange 2| adapted to seat on the disk 8, but normally. held off this seat by the spring l8.

Numerals 22 and 28 indicate electric leads which are connected to a battery. Conductor 23 is connected to a stud 24 passing through disk I said metal reaches a predetermined value the switch will close and actuate the signalling means.

Further objects and advantages of the present invention will appear from the accompanying drawing in which- Fig. 1 is a longitudinal section of a device according to the present invention; and

Fig. 2 is a diagrammatic illustration of the electrical circuit in said device.

Referring to the drawing in detail, numeral I designates a tubular metal case, preferably of about the size of a fountain pen, having mounted at the lower end thereof a cap 2 which is pro-v vided with an outwardly extending knob 3, having an internal recess or well 4. The element 2, or' at least the lower end thereof, that is the bottom surface of the well, .is preferably made-of soft ironof high magnetic permeability. Screwed into the innerface of the head 2 is an elongated tube of soft iron 5 which constitutes the core of a solenoid 6. The upper end of the tube 5 is held in place by a washer 1 of insulating material.

Above washer 1 is a metal disk 8 held inplace on washer 1 by a flange! of insulating material which forms the lower end of a tubular me'mber l0 having an inner bore coextensive with the bore in tube 5 and having at its upper end another and flange 9 as well as through the disk 8. Also passing through the disk is a stud 25, to the lower end of which is connected one element 26 of a contact. The other element 21 of this switch is connected to one terminal 28 of the solenoid.

The two elements, 26 and I1, form a seat for a metal button 29, which is normally held of! this seat by a spring 30. The other lead22 is con-' nected to the other terminal 3| of the solenoid and is also connected to a conductor 32 to the light socket.

With the parts in the position shown the button 29 is depressed and closes the solenoid circuit, thereby magnetizing the iron rod 28. The lower end of this rod is spaced from the bottom of the well 4 a. short distance corresponding to the distance between the flange 2i and the disk 8.

, When the knob 8 is placed against the metal the magnetic permeability of which is to be tested, and the magnetic permeability of this metal reaches a predetermined value, the rod will'be attracted to the metal, and will'move to the bottom of the well, thereby bringing flange 2| onto the disk 8 and closing the light circuit,- spring l8 forming one of the conductors in this circuit. Thus, when the magnetic permeability of the metal being tested reaches the predeter x i, mined value the light will flash. What the mag-Q netic permeability of the metal must be in order to work the signal is determined by-the strength of the spring l8.

In practice the spring is so selected that it will permit closure of theswitch when a weld reaches the critical point in its cooling stage. Thus, as 5 soon as the weld is completed the knob 3- isplaced against it and when the light flashes operator knows that it is safe to quenchthe weld.

It will be apparent that changes may be made in the specific embodiment described 'above. which is presented only for purposes of illustration, without departing from the scope of the present invention. Such changes as are within the skill of the artisan are contemplated within the scope or the appended claim in which it is intended to claim the present invention as broadly as the prior art permits.

I claim:

A hand device for testing welds comprising a pair of concentric tubular members, a head on said members having a metal surface adapted to be placed against the weld to be tested, a wellin 1(Ladapted to be operated by movement of said magnetic element into said well.

WILLIAM A. BRUCE. 

